The present invention relates generally to the field of tubing couplings and, more particularly, to a tube sealing bushing which enables an appropriate grip to be taken and held on tubing which is inserted through the bushing to seal the tubing to a body. It is especially effective with small tubing. For instance, it finds usefulness with tubing which measures a nominal 0.0625 inches to 0.125 inches in diameter, for example. This size of tubing finds great application in chemical test laboratories where it is necessary to connect together several pieces of equipment with tubing.
The bushing of the present invention cooperates with a male nut which is threaded behind the bushing to drive a face of the bushing into a flat bottom detail. The term xe2x80x9cdetailxe2x80x9d applies to the mating surface of the body which receives the bushing. Tubing this small is commonly used with chemical test instruments for small fluid samples. Such instruments include a gas chromatograph and the output equipment connected to it. Suitable valves, switches, accumulators, pumps, and other paraphernalia are well known in chemical test laboratories. All these components are connected together with tubing of the size discussed in this disclosure.
All of this tubing and the various connections have to be made in a tight, leak proof manner. Moreover, the tubing in all instances has to be sealed in such a way that flow is not unduly impeded. Over-crimping of the tubing is probably not a difficulty with one inch tubing and other large sizes. It is much more noticeable in small diameter thin wall tubing such as 0.0625xe2x80x3-0.125xe2x80x3 diameter tubing. The tubing may be made of soft plastic and the makeup pressure on the tubing may tend to damage the end of the tubing. The difficulty with crimping near the end of the tube is that the tube is so small that is hard to see with the unaided eye whether or not the tube has been damaged. In thick wall tubes, that is not much of a problem. In the small tubes commonplace in a chemical test laboratory, it is a problem in the sense that it restricts flow. For that reason, it is desirable to use the bushing of the present disclosure so that the tubing connection can be made in a less damaging manner.
The present disclosure is directed to a bushing constructed with a pair of annular, v-shaped external grooves. The bushing is preferable made of a plastic material to enable plastic flow of the bushing. This changes the grip held by the bushing on the tubing so that the grip is accomplished at the grooves and also spaced back along the tube at the large diameter of the bushing.
In a first aspect, the present invention provides a tubing connection with a plastic bushing. The bushing is made of a deformable plastic including an elongate cylindrical body into which a pair of annular, v-shaped grooves are cut or otherwise formed. The grooves clamp the bushing against the tube that is inserted through the bushing, and thereby resist collapsing the internal passage in a way that damages the tubing. It has been determined that the controlled crimp which is provided by this system is a limited crimp, thereby enhancing the leak sealing performance of the bushing. Enhanced performance includes longer life and the ease of repeated use of the end of a tube as would occur in connecting and disconnecting the tube from an instrument.
In this first aspect of the present disclosure, the bushing is constructed with an alignment flange on the end of the bushing that is inserted into the instrument. The alignment flange mates with a complementary through-hole in the instrument body to align the bore of the tubing with a port in the instrument. The alignment flange is preferably, included with the bushing when sealing smaller diameter tubing, such as 0.0625xe2x80x3 tubing, to an instrument. For 0.125xe2x80x3 tubing, the alignment flange is eliminated, and the maximum outside diameter of the bushing mates with the minor diameter of the detail.
In a further aspect of the invention, a bushing is provided which includes a pair of V-shaped annular grooves separated by a V-shaped land. This bushing or collapsible bushing is particularly suited for {fraction (1/32)}xe2x80x3 to xc2xcxe2x80x3 O.D. tubing and for use with fittings or nuts with mating threads. This bushing collapses when compressed by a mating nut. When used on smaller size tubing, a counterbore in the mating nut receives the end of the bushing. For, larger sizes of tubing, such as 0.125xe2x80x3 tubing, the counterbore is unnecessary. As the mating nut presses the bushing into the receiving port of the instrument and the bushing collapses, the collapsed area is pressed into the outside of the tubing, effecting a very secure connection.
This coupling structure is preferably made of a material which varies with the tubing on which it is used. Examples include polyetheretherketone (PAEK), Teflon, FEP, and Tetzel. When used with small ID Teflon or FEP tubing, by sealing in a very small area with the structure of this invention, a tendency to reducing tubing I.D. is greatly minimized.